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Some suggest there might be alien aircraft on Earth now. The argument goes something like this:

(1) A priori, there’s no reason there shouldn’t be alien aircraft. Earth is 4.54 billion years old, but the universe is 13.7 billion years old, and within a billion light years of Earth there are something like 5 × 10¹⁴ stars. Most of those stars have planets, and if an alien civilization arose anywhere and built a von Neumann probe, those probes would spread everywhere.

(2) We have tons of observations that would be more likely if there were alien aircraft around than if there weren’t. These include:

  • Vast numbers of anecdotal reports from pilots.
  • Videos that appear to show objects with flight characteristics far beyond known human capabilities.
  • Senators—with access to classified information—raising concerns about unknown craft near military installations.
  • Rumors from multiple sources that the government has captured, intact alien craft.

(3) So if we agree that:

then don’t we have to conclude that the posterior probability P[aliens | everything] is pretty high?


What I like about this argument

First, I agree the prior probability should be pretty high. Say you just told me:

Okay, say there’s a universe with at least 10²⁴ stars, and most stars have planets, and on one planet somewhere life has evolved and started sending stuff to other planets and has an ever-accelerating pace of technological development.

Then I would agree—the odds that there would be alien aircraft on my planet seem good. It seems like we—or our artificial descendants—might well send aircraft to other planets. So why shouldn’t alien aircraft be here, now?

Second, it takes eyewitness reports seriously. There are a huge number of reports by pilots seeing objects accelerating at insane rates with no obvious wings, control surfaces, or signs of propulsion. It’s a mistake to dismiss these as a product of diseased minds or attention-seeking. There are just too many reports—both civilian and military—sometimes from pilots in different planes at the same time, sometimes invisible to radar and sometimes confirmed by radar from multiple sources. Usually, these people make little effort to draw attention to themselves—we only hear about their observations secondhand. They seem serious and well-intentioned.

(I hesitate to mention this, but I even have family members that report seeing something very strange years ago. I respect their intelligence and I don’t think they have an agenda—they barely talk about it and don’t consider it very important. The story goes that I myself saw it, but I was very young and remember nothing.)

Third, I agree that lots of these observations are very hard to explain. Now, of the 510 reports investigated for the 2022 UAP task force report, more than half had mundane explanations—usually balloons or drones. And some of the leaked videos could plausibly be explained in terms of stuff like rotating glare. But other incidents have apparently been measured by different sensors (e.g. vision, radar) or from multiple locations (e.g. a plane and a ship) simultaneously, and just don’t have a clear conventional explanation.

Fourth, I think this argument correctly rejects some of the other explanations people give for these observations. Some say these are real observations, just coming from human aircraft built in some highly classified (American? Chinese? Russian?) program. For some observations, that’s plausible. But I think it’s extremely unlikely a government has built a tic-tac that can accelerate at 700 gravities with no visible wings or propulsion. I don’t think governments are competent enough to develop technology so many generations ahead of what’s publically known—in this case involving new physics—all while keeping it completely secret. There are no historical examples of anything like this. (The Manhattan Project is probably the closest analogy, but even then many scientists around the world knew such a thing might be possible.)

Or, some people say that it’s disinformation—all the reports and videos are fake, and the US government is putting them out to confuse adversaries into thinking that it must be a classified program, and therefore the US must have secret alien-level technology. That’s… quite a theory. I mean, what’s the incentive? Does China worry about the US sending in the tic-tacs when they make plans to invade Taiwan? And why the reports in other countries around the world? It would be a massive conspiracy for a tiny benefit.

And finally, I’m a Bayesian extremist. If I do a calculation and I get weird results, then I’ll check my calculations. But ultimately, I’ll accept the results.

For simplicity, let’s say the prior probability that there could be alien aircraft is 50%, i.e.

    P[aliens] = P[no-aliens] = 0.5.

And let’s say that the probability that multiple civilian pilots would all report seeing a tic-tac at the same time is nine times higher with aliens than without them, i.e.

    P[tic-tac | aliens] = 0.09

    P[tic-tac | no-aliens] = 0.01

Then an easy calculation gives that, conditioning on the tic-tac report, there's a 90% chance of aliens, i.e.

    P[aliens | tic-tac] = 0.90

I accept all that. But I still think aliens are very unlikely.

Is Bigfoot fucking with us?

If you’re not from North America, you may not be aware of Bigfoot—this big furry human-ish guy said to roam around in forests:


Now, I don’t want to compare believing in alien aircraft to believing in Bigfoot. You might argue that Bigfoot is less plausible, a priori. But regardless of that, the evidence for Bigfoot isn’t close to the evidence we have for weird stuff in the sky.

Never mind that. All I want to talk about is: Up until the 1990s or so, a lot of people seemed to take Bigfoot seriously. But today, almost no one does. Why?

Has society become more rational? Has Bigfoot just fallen out of fashion? Maybe, a little, but I don’t think that’s why.

No, the answer is simple: Today, there are cameras everywhere. Back in the 1960s, you might take some random grainy film footage kind of seriously, because not that many people were taking movies in the deep woods. But today? There are people hiking in the woods with cameras everywhere and no one has ever recorded a close-up video of Bigfoot.

If Bigfoot exists, then he’s monitoring our technological development and now hiding away more carefully, so we never get definitive proof. (He still makes time for lots of people who are incapable of taking their phones out of their pockets.) That seems unlikely, right?

So it’s not that we got evidence against Bigfoot. It’s that the lack of incontrovertible evidence has become damning.

Against alien aircraft

So what’s wrong with our initial argument?

First of all, lots of the old observations that seem to suggest alien aircraft turned out to be wrong. We now know that Roswell was a government coverup—but of high-altitude balloons with microphones to pick up Soviet atomic bomb tests, not aliens. Half of reports end up being shown to be weather balloons.

Beyond that, many other reports probably have mundane explanations we just haven’t found. The 2022 UAP task force attributed 6 of 510 reports to “clutter” like birds, weather events, or—somehow—plastic bags. But how good are our records for birds or plastic bags? It sure seems like if clutter caused a report, we have low odds of being able to attribute it to clutter. So surely clutter explains some of the other reports, too.

Second, all these observations are not independent. If a sensor glitch can happen in one place, it can happen in other places. If some natural weather phenomena can look like physics-defying tic-tac once, it can do that again. Beyond some level, the sheer number of reports just doesn’t add that much additional evidence.

Finally, and most importantly, you have to condition not just on what we see, but what we don’t see. We get grainy videos of some weird thing in the distance, but never close-up HD video. Pilots report seeing something flying far away, but it’s always far away—the tic-tac never flies up close to a passenger jet so hundreds of people can look at it in detail. We get rumors that the government has clear high-resolution pictures, but they never get leaked. We get rumors that the government has recovered intact alien aircraft, but it’s always someone who heard someone else talking about it—we never have a whistleblower who actually analyzed the aircraft and can tell us what they’re made out of. There’s never a local government—anywhere in the world—that captures an aircraft and posts photos online.

Across every dimension in which we could get evidence of aircraft, we see “everything that’s possible to see if alien aircraft didn’t exist”, but never more. There are many opportunities for a smoking gun, but we never get one.

If you want to calculate the probabilities correctly, you have to condition not just on the observations, but also on the ungodly number of observations that we don’t have—on the “billions of guns that failed to smoke”.

If alien aircraft were on Earth, they would need to be carefully calibrated to give us grainy distant glimpses (in every possible way) but never more. If alien aircraft are here, they’re screwing with us.

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Bigfoot is arguably less plausible, a priori.

Is it? A priori, Bigfoot is just some unknown small population of a large mammal living in a remote forest, possibly a living fossil of, e.g., a giant ground sloth species. That's more possible than alien crafts. Not alien life, mind you, but crafts require interstellar travel to be plausible, and we have reason to doubt that. Even unmanned Von Neumann probes would have a very hard time arriving to their destination still functioning (never mind braking...), and non-inertial engines presume a violation of known physics so deep, it's unbelievable we've missed all signs of it being possible until now.

I would even argue that Bigfoot being more bigfooty; a primitive yet sapient and inteligent hominid, perhabs some late descendant of the gigantopithecus, is more plausible than it being say a sloth, because it seems to make honest attempts to avoid humans. If it was a mere sloth, or an ape oof the same intellectual capacity as a chimp, it would be found far easier.

While existence of Bigoot is extremely unlikely, If it were real, I would rather assume they are a tribal species of essentially very hairy humans who avoid us the same way some Sentinel tribes do.

You've convinced me! I don't want to defend the claim you quoted, so I'll modify "arguably" into something much weaker.

Also perhaps of interest might be this discussion from the SSC subreddit awhile back where someone detailed their pro-Bigfoot case.

I'm the OP of that bigfoot discussion on r/ssc. My views haven't substantially changed on that subject.

I agree with the great-grandparent that aliens being real is an enormously bigger change from the standard worldview than bigfoot being real.

I give < 10% likelihood to these UAPs being genuine aliens as stereotypically imagined, and < 50% likelihood of being some significant scientific update (e.g. weather phenomenon, spoofing technology).

However, assuming actual aliens in spaceships were here and trying halfheartedly to hide from us, I would expect the photo and video evidence to be about as crap as it is. So I agree with the conclusion of this OP, but disagree with the rationale.

Edit 19-JUN-2023: Upon reflection, I think assigning <10% likelihood is overconfident of me. I realized this when I read the recent post asking for UAP bets and thought about the real reasons why I wouldn't take the bet.

trying halfheartedly to hide from us

The aliens are here and they're super advanced, but they're also kind of klutzes.

Not alien life, mind you, but crafts require interstellar travel to be plausible, and we have reason to doubt that. Even unmanned Von Neumann probes would have a very hard time arriving to their destination still functioning (never mind braking...), and non-inertial engines presume a violation of known physics so deep, it's unbelievable we've missed all signs of it being possible until now.

While I agree with your general argument, I would like to point out that the aliens don't have to be from another star system. 

It seems that our Solar System has at least a dozen of separate places that could harbor life, from the clouds of Venus to the possible subsurface oceans of Pluto and beyond. And the list mostly considers the life that is similar to our own, requiring warm water (and not, say, solitons of the solar plasma). Extending the list with truly alien forms of life could increase the number of possible cradles to perhaps two dozens (??) in our Solar System alone. 

Additionally, perhaps humans are not the first species on Earth that has created a technological civilization. So, theoretically there could be aliens originated from Earth. 

Other lifeforms in the solar system? Sure. Other technological civilizations that we somehow haven't detected? Waaaaaay unlikely.

Thanks! I once wrote up a somewhat-parallel discussion on a different topic in Section 5.1 here:

… So this is the “null hypothesis” of what to expect if there’s no such thing as [blah]. By now there are probably ≈1000 person-years of experimental data created by [blah] researchers. In such a huge mountain of data, there is bound to be lots of “random noise and ad hoc misinterpretations” that happen to line up remarkably with researchers’ prior expectations about [blah]. The question is not “Are there results that seems to provide evidence for [blah]?”, but rather “Is there much more evidence for [blah] than could plausibly be filtered out of 1000 person-years of random noise, misinterpretations, experimental errors, bias, occasional fraud, gross incompetence, weird equipment malfunctions, etc.?” …

and I also linked to & excerpted yet another parallel discussion on yet a different topic by Scott Alexander, Section 17 here.

Scott Alexander post that seems very relevant to your example: The Control Group Is Out Of Control. It puts into question even the heuristic of "Is there much more evidence for [blah] than...".

I think you're starting with the wrong prior.  It's very distantly relevant whether there are aliens in the universe (or even in our past lightcone).  It's important what is the prior for "aliens physically present on earth, now, at a scale (quantity and size) and tech level that makes them very intermittently and unreliably detectable".  The second is orders of magnitude smaller than the first.

I do agree with your logic about the inequalities, but the magnitude of difference matters a lot.  I give pretty low values for p[whistleblower|aliens] - p[whistleblower|no aliens] and the like, EVEN WHILE agreeing that it's greater than zero.

I agree with your conclusion, including the fact that we need some value for p[aliens that could easily remain hidden, but are screwing with us], and that this may even be the majority of the weight for p[our observations|aliens].  

But is it necessarily unlikely that they would be screwing with us if they existed? That's something I don't like about the bigfoot comparison, it's obviously laughable that large apes are evading camera detection at every turn, but with aliens, presumably it would be trivial to do so. We know that they would have the means, so that only leaves the reasoning to do this. I also don't necessarily agree with the assumption that our commercial sensor tech is good enough to detect hypothetical aliens. Try filming a drone from a distance with your phone. It will look surprisingly unclear. Modern cameras are obviously more than adequate to film a bigfoot but I don't think so for aliens-the sky is big etc. 

What I didn't get from your post is how the prosaic sensor anomalies/atmospheric oddities and statistical artifacts etc lends itself to explaining the much more zany claims that are now coming out of intelligence and intelligence connected people. It doesn't seem to explain someone claiming there are actual recovered bodies/craft, at all. My take on that is the psyops/disinfo angle you wrote off becomes much more likely. 

Given real aliens, they would need to either have capped tech or actively trolling to explain even low quality observations or pieces of craft. Nonintervention laws and incorrigible global anti-high-tech supervision constraining aliens are somewhat plausible, coordinated trolling less so.

Given real aliens, how can you be sure of making any claims at all about their civilization/technology/culture/anything without having the sort of observational evidence that would be necessary to make such claims? 

We're in Cartesian Demon territory when discussing these theoretical others. We can plop our human notions on top of them all we want, but unless we have direct, observable evidence of the way "they" think/operate/whatever, we can just as easily assume any given conclusion about them as just as likely as any other. And that includes all the N conclusions we haven't even thought of (or simply can't conceive of due to our necessarily human viewpoint).

It seems wildly overconfident to make any claims about them at all that aren't completely hypothetical in the way you describe in your other reply here. Your idea that they either have to have capped tech or be actively trolling is itself just a hypothesis at best, and an idea at worst.

All filtered evidence is good for is formulating hypotheses, or even just inspiring ideas that are not hypotheses.

We can consider whatever, there is no fundamental duty to only think in particular ways. The useful constraints are on declaring something a claim of fact, not muddying epistemic commons or damaging decision relevant considerations; and in large quantities, on what makes terrible training data for the brain, damaging the aspects with known good properties. Everything else is work in progress, with boundaries impossible to codify while remaining on human level.

Some thinking processes seem to be more useful for arriving at true or useful results; paying attention to that property of processes is rationality. This doesn't disqualify processes of which we know less, that would be throwing away the full current force of your mind.

The other comment is about updating and credences. I'm not engaging in updating or credences in this thread.

I don't think I have any argument that it's unlikely aliens are screwing with us—I just feel it is, personally.

I definitely don't assume our sensors are good enough to detect aliens. I'm specifically arguing we aren't detecting alien aircraft, not that alien aircraft aren't here. That sound like a silly distinction, but I'd genuinely give much higher probability to "there are totally undetected alien aircraft on earth" than "we are detecting glimpses of alien aircraft on earth."

Regarding your last point, I totally agree those things wouldn't explain the weird claims we get from intelligence-connected people. (Except indirectly—e.g. rumors spread more easily when people think something is possible for other reasons.) I think that our full set of observations are hard to explain without aliens! That is, I think P[everything | aliens] is low. I just think P[everything | no aliens] is even lower.

As for Bigfoot: while I don't believe it exists, I think Its wrong way to think of it as avoiding cameras. The more reasonable explanation is that cameras avoid the places where it could possibly live. Bigfoot, Sasquatch, Yeti, and similar Apemen are almost always reported to live in remote wilderness, and specifically the North of USA, Canada, Russia, China, and of course the Himalayas. It seems like we should be able to spot them, until you realize that the northern wilderness belt that stretches from Alaska to Greenland, and then around Eurasia and back to Alaska is astonishingly big, and almost completely empty of humans. We are talking about a strip of wilderness that has about the same surface area as the Moon, and the possible population of Bigfeet would likely be smaller than the population of chimps in Africa. If every researcher interested in finding Bigfoot went to explore the Big North with all the state of the art equipment they could carry, and they spread evenly to cover maximum area, they would not only not find Bigfoot, but not find each other, due to enormous distances through impassable woodland and mountains. 

The problem is that prior to ~1990, there were lots of supposed photographs of Bigfoot, and now there are ~none. So Bigfoots would have to previously been common close to humans but are now uncommon, or all the photos were fake but the other evidence was real. Plus, all of that other evidence has also died out (now that it's less plausible that they couldn't have taken any photos). So it's possible still that Bigfoot exists, but you have to start by throwing out all of the evidence that people have that Bigfoot exists, and then why believe in Bigfoot?

Still, over time it should become more likely to meet Bf, not less; there are more people in general, and more documentary filmmakers, adventurers, tourists, infrared cameras, planes etc

Except if they died out. However, someone should at some point also find bones.

It is quite possible though that over time there are fewer and fewer BFs. They might be going extinct, even without much human interaction. As for finding bones, if the population is low, and their territory so big, it might take centuries. 

Expanding a comment I made in the other thread, take a look at the Wikipedia list of reported UFO sighthings. One thing that I immediately note scrolling this list is that the overwhelming majority of reports after 1950 are from the US. The last time aliens were sighted in Italy was 1978. In France, 1981. In Spain, 1979. Germany does not appear on the list at all. On the other hand, there are 42 entries for the US and the list is not even updated.

My priors on "UFO sighthings are a culture-bound illness of the US" are significantly higher than "Not only there are aliens but they are mostly ignoring everything outside America". 

I also noticed that there is an inverse cultural relationship between the belief in magic, witchcraft, spirits/fair folk etc and the belief in UFOs. Which makes me think aliens simply fill the Post-Enlightment gap in the legendarium for cultures that want to pretend they are "too reasonable" to beleive in magic, but open to a belief in "sci fi" myths; ie: Fair Folk kidnapping folk - nah, Aliens kidnapping folk - yah.

I can assure you that list is US centric. There are plenty of reported sightings in all of Europe in the last 30 years.
The 90s especially and there are several 'mass sightings' that I've read about in Portugal that are simply not in that list.
There is a clear lack of centralized information about all the world ufo reports, even if their explanation is prozaic.

I know that the mainstream view on Lesswrong is that we aren't observing alien aircraft, so I doubt many here will disagree with the conclusion. But I wonder if people here agree with this particular argument for that conclusion. Basically, I claim that:

  • P[aliens] is fairly high, but
  • P[all observations | aliens] is much lower than P[all observations | no aliens], simply because it's too strange that all the observations in every category of observation (videos, reports, etc.) never cross the "conclusive" line.

As a side note: I personally feel that P[observations | no aliens] is actually pretty low, i.e. the observations we have are truly quite odd / unexpected / hard-to-explain-prosaically. But it's not as low as P[observations | aliens]. This doesn't matter to the central argument (you just need to accept that the ratio P[observations | aliens] / P[observations | no aliens] is small) but I'm interested if people agree with that.

I make no claim to speak for anyone who isn't me, but I agree with your analysis. I would say similar things about e.g. ESP and miracles and the like.

I think the evidence against (most) miracles is stronger because they violate the laws of physics. Although I think the same could be said for a few UAPs--if a UAP moves in a way that is physically impossible as far as we know, that's strong evidence against it being aliens, because aliens still have to follow the laws of physics.

How would a tic-tac to accelerate at 700g with no visible propulsion, even positing the existence of super-advanced technology? The best I can think of off the top of my head is that it's using an extremely strong magnet to manipulate its position relative to earth's magnetic field. But that would require an absurd amount of energy so it would probably need to be powered by a tiny cold fusion reactor (which may be physically impossible), and it would still need to avoid emitting noticeable amounts of heat, and even if it has some sort of hyper-insulating shell, it would need internal parts that don't evaporate under that much heat, and also need to avoid emitting the massive amount of heat that would be generated by friction with the air.

You do your argument a disservice when you conflate "laws of physics" with "extrapolations of current materials and energy engineering".  

If speed of light isn't violated, and the force involved isn't so great that the reaction would be measurable as changes in earth rotation or something, and the energy is much less than the theoretical limit of a small amount of antimatter, it's not "laws of physics" that is the constraint.

Note I'm not saying you're wrong in considering it very unlikely, but hyperbole doesn't help in thinking or in discussion (here on LW, at least - it's common and perhaps useful in other contexts).  

Ok, fair point, I was going too far in assuming that the sort of engineering necessary was physically impossible.

Even if there are aliens, and humans do sometimes gain data showing such, if the aliens are sufficiently advanced and don't want to be found, I would not be surprised if they selectively took away our conclusive data but left behind the stuff that's already indistinguishable from noise. Kinda like how we take our trash with us after hiking and camping, but don't worry too much in most places about our footprints or the microscopic bits of material our gear and bodies leave behind.

Glitches happen. Misunderstandings happen. Miscommunications happen. Coincidences happen. Weird-but-mundane things happen. Hoaxes happen. To use machine learning terminology, the real world occurs at temperature 1. We shouldn't expect P[observations] to be high - that would require temperature less than 1. The question is, is P[observations] surprisingly low, or surprisingly high for some different paradigm, to such an extent as would provide strong evidence for something outside of current paradigms? My assessment is no. (see my discussion of Nimitz for example)

Some additional minor remarks specifically on P[aliens]:

  • non-detection of large (in terms of resource utilization) alien civilizations implies that the density of interstellar-spacefaring civilizations is low - I don't expect non-expansion to be the common (let alone overwhelmingly selected) long term choice, and even aestivating civilizations should be expected to intervene to prevent natural entropy generation (such as by removing material from stars to shut them down)
  • If the great filter (apart from the possible filter against resource-utilization expansion by interstellar-spacefaring civilizations, which I consider unlikely to be a significant filter as mentioned above) is almost entirely in the abiogenesis step, and interstellar panspermia isn't too hard, then it would make sense for a nearby civilization to exist as Robin Hanson points out. I do actually consider it fairly likely that a lot of the great filter is in abiogenesis, but note that there needs to be some combination of weak additional filter between abiogenesis and spacefaring civilization or highly efficient panspermia for this scenario to be likely.
  • If a nearby, non-expanding interstellar-spacefaring civilization did exist, then of course it could, if it so chose, mess with us in a way that left hints but no solid proof. They could even calibrate their hints across multiple categories of observations, and adjust over time, to match our capabilities. However, I don't think them choosing to do this is particularly likely a priori. If someone assumes that such aliens exist and are responsible for UAPs, while also noting that we haven't seen clear proof of their existence, then their posterior may assign a high probability to this - but I would caution against recycling the posterior into the prior.

(Edit: switched things around to put the important stuff in the first paragraph)

The general point that you need to update on the evidence that failed to materialize is in the sequences and is exactly where I expected you to go based on your introductory section.

I see a lot of people commenting here and in related posts on the likelihood of aliens deliberately screwing with us and/or how improbable it is that advanced aliens would have bad stealth technology or ships that crash. So I wanted to add a few other possible scenarios into the discussion:

 - Earth is a safari park where people go to see the pristine native wildlife (us). Occasionally some idiot tourist gets too close and disturbs that wildlife despite the many very clear warnings telling them not to. (Anyone who has ever worked with human tourists will probably have some sympathy for this explanation.)

 - Observation of Earth is baby's first science project. High-schoolers and college undergrads can practice their anthropology/xenology/whatever on us. Yes, they're supposed to keep their existence secret from the natives, otherwise it wouldn't be good science, but they're kids with cheap disposable drones and sometimes they screw up.

 - There is a Galactic Federation with serious rules about not disturbing primitive civilisations (us), and only accredited scientists can go observe them, but even scientists get bored and drunk and sometimes do dumb stuff when they're on a low-prestige project a long way from any supervisors. 

Obviously, these are all human-inspired examples, aliens could have other motivations incomprehensible to us. (Imagine trying to explain a safari park to a stone-age hunter-gatherer. Then remember that aliens potentially have a comparable tech gap to us and non-human psychology.) 

Some takeaways from the scenarios above:

  1. Aliens aren't necessarily monolithic. There may be rule-setting entities (whoever says 'don't go near the wildlife') which are separate from rule-following entities, and rules about not bothering Earthlings may not be maximally enforced. 
  2. We shouldn't assume we're seeing their most advanced tech. Human beings can manufacture super-safe jet planes that approximately never crash. We still build cheap consumer drones that sometimes fall out of the sky. Saying "how come an ultra-advanced alien civilisation can't build undetectable craft?" is like looking at a kid whose drone just crashed in a park and saying "you'd think humanity could build planes that stay in the air". We can. We just don't always do it, nor should we.
  3. We shouldn't assume they care that much. Whoever is in charge of enforcing the rules about "don't bother earthlings" might be the equivalent of a bored bureaucrat whose budget just got cut and who gets paid the same whether or not they actually do their job. Or a schoolteacher who's more interested in getting the kids to complete their project than in complying with every pettifogging rule that no one ever checks anyway. 


I realise all the above makes it sound like I believe in aliens, so for the record, I think that Chinese drones or other mundane causes are the most likely explanations for American UAP reports, and that hoax/disinformation-op/mental-breakdown are the most likely explanations for the Grusch whistleblower claims. But I would put about a 10% probability on actual aliens, which I realise is a lot higher than most LessWrongers.

I'm curious, have you seen the 4chan leak before writing this (if you don't mind answering)?

I had not, and still don't know about it, can you post a link?

Personally, I think there are almost certainly no extraterrestrials here, so I'm not sure the 4chan post is worth reading. (I was just wondering whether the common elements were inspired by it or not.)

Anyone who is confident no ufos are truly anomalous, please feel free to extend me odds for a bet here

I have already paid out to two betters so far, and would like some more

"If alien aircraft were on Earth, they would need to be carefully calibrated to give us grainy distant glimpses (in every possible way) but never more. If alien aircraft are here, they’re screwing with us."

I don't know - this inference seems rather weak. I try to be on time to appointments, most of my failures are pretty small - observing me being late a minute or two a couple of times does not mean that I calibrate being late to a minute or two. Failures would naturally cluster near the border line.

Plus they might be actively erasing evidence when it is too obvious.

This is not about alien aircraft, this is just a completely wrong way to approach updating. The set of observations/experiments being evaluated is filtered by what was actually observed and by the narrative around the hypothesis (which is in turn not independent from what was actually observed). There are other potential observations that didn't happen, and that fact is also evidence, and yet more observations that did happen but aren't genre-appopriate. By not updating on these other potential observations, the evidence is heavily filtered, and so updating on what remains is of no use at all in estimating how much weight to put on any given hypothesis.

All filtered evidence is good for is formulating hypotheses, or even just inspiring ideas that are not hypotheses. If you do formulate a hypothesis, it's then necessary to carefully think about which potentially observable things would be predicted by it, compared to its alternatives, in worlds reframed from within the hypotheses (at which point the noise of fake evidence gets a reckoning, and absence of evidence manifests as evidence of absence). Even that risks privileging strange hypotheses, but at least we can fight that with priors. Very strange hypotheses don't give useful predictions of observable things, so they probably shouldn't even count as hypotheses in the context of credences and updating.

Agreed that paying attention to how evidence is filtered is super important. But, in principle, you can still derive conclusions from filtered evidence. It's just really hard, especially if the filter is strong and hard to characterize (as is the case with UAPs).

Sure, but that's not about formal-ish updating that frames this post, where you are writing down likelihood ratios and computing credences.

Fair enough. (though...really you could in principle still handle filtered evidence in a formalish way. It just would require a bunch of additional complication regarding your priors and evidence on how the filter operates).

Yeah, I thought to note that in the comment that starts this thread; that's not the kind of thing that seems practical when coordinating updating in an informal way. So more carefully, the intended scope of the comment is formal updating (computing of credences) that's directed informally (choosing the potential observations and hypotheses to pay attention to).

I think the prior for aliens having visited Earth should be lower, since it a priori it seems unlikely to me that aliens would interact with Earth but not to an extent which makes it clear to us that they have. My intuition is that its probably rare to get to other planets with sapient life before building a superintelligence (which would almost certainly be obvious to us if it did arrive) and even if you do manage to go to other planets with sapient life, I don't think aliens would not try to contract us if they're anything like humans.

Finally, and most importantly, you have to condition not just on what we see, but what we don’t see. We get grainy videos of some weird thing in the distance, but never close-up HD video. Pilots report seeing something flying far away, but it’s always far away—the tic-tac never flies up close to a passenger jet so hundreds of people can look at it in detail. We get rumors that the government has clear high-resolution pictures, but they never get leaked. We get rumors that the government has recovered intact alien aircraft, but it’s always someone who heard someone else talking about it—we never have a whistleblower who actually analyzed the aircraft and can tell us what they’re made out of. There’s never a local government—anywhere in the world—that captures an aircraft and posts photos online.

I'm not sure about this reasoning. It seems compelling at first (and is my personal strongest reason against believing the latest rumors), but there's a sort of anthropic issue where if we already had compelling evidence (or no evidence) we wouldn't be having this discussion. Is there a prior for the likely resolution of fuzzy evidence in general? Maybe the issue is a lack of an observed distribution of mostly weak and some stronger evidence, rather than all weak?

there's a sort of anthropic issue where if we already had compelling evidence (or no evidence) we wouldn't be having this discussion.

Yes, our discussion is based on the evidence we actually see. But, to then discount the evidence because if we had different evidence we wouldn't be having the same discussion, is to rule out updating on evidence at all, if that evidence would influence our discussion.

Is there a prior for the likely resolution of fuzzy evidence in general?

In my view, there is a general tendency to underestimate the likelihood of encountering weird-seeming evidence, and especially of encountering it indirectly via a filtering process where the weirdest and most alien-congruent evidence (or game-of-telephone enhanced stories) gets publicly disseminated. For this reason, a bunch of fuzzy evidence is not particularly strong evidence for aliens.

If by 'very unlikely' you think the likelihood is <1% you can get nearly free money by betting against:

I think the user is still willing to send out a few thousand dollars.

The obvious (and not by any means new) knock-down argument against aliens is the lack of correlation between increased ubiquity of hi-res cameras everywhere and better res images of UAPs. 

The biggest problem with the argument is that, given our current knowledge about the specific details of extraterrestrial civilizations, the term 'aliens' in P[aliens] does not fulfill the hard-to-vary criterion of a good explanation.

Skeptic: "If it's aliens, why haven't they been trying to contact us"  
Post-hoc variation: "Because of the Prime Directive"

Skeptic: "If it's a physical vehicle, why does it not obey the laws of physics"
Post-hoc variation: "Because the aliens have discovered new physics which we don't know about".

etc.. etc..

Any unexplained phenomena, terrestrial or otherwise, can be explained by 'aliens', and for any skeptical counter-argument, the specifics of 'aliens' can be varied to fit the facts.  

Therefore, as things stand with our current knowledge, 'aliens' is simply not a good explanation, regardless of the prior and posterior probabilities.

If aliens are here, they are definitely screwing with us by remaining covert. I don't know how that figures into the odds given the evidence. It would require incompetent aliens, or else aliens so competent that they could judge how much crappy contact data would make the whole thing seem so unlikely that it gets ignored by most rational people.

Like me.

If they're here but not willing to make contact, they're useless to me as far as I can tell, and I'll go on doing the same things whether or not they exist.

One piece of the logic that I do find interesting is the interaction with AGI x-risk. If aliens were here, they probably wouldn't want us creating a light-cone swallowing misaligned AGI.

If we're talking about highly unexpected phenomena, then I think that this analysis is putting the cart before the horse. Look at it this way: The theory of materialism (in all of its forms) pushes us toward the idea that there is a sharp distinction between the mental and the physical. That is to say, it pushes us toward thinking that what exists objectively exists in space and time from the point of view of all observers and that what doesn't meet those criteria is a hallucination. However, we are already familiar with phenomena that fall in between the cracks of those distinctions. The best example is a rainbow. 🌈 We speak of rainbows as though they had an extent in space — and indeed, we can take photographs that seem to prove that to be true — yet, their extent in space is illusory because it changes with every (physical) point of view. As we know, no person has ever yet found the end of a rainbow. Nevertheless, if you are standing next to me, I can point to a rainbow and you will see it. Thus, with respect to how the phenomenon maps onto our language, it is impossible to answer the question of whether it has an objective physical existence. We grant rainbow the status of having an objective physical existence because they can be studied in a laboratory. However, if we are discussing phenomena of a more exotic nature, phenomena that we have not been able to study in a laboratory, then we should acknowledge the possibility that complications in our ability to map language onto reality could create problems when we attempt to use Bayesian probabilistic reasoning.

I guess that my point is that the question of whether "alien aircraft" physically traveled from another planet to Earth is a different question than whether there was an "intelligently controlled shared hallucination". And if you are an idealist (as opposed to a materialist), then you might say that everything we collectively see and can objectively measure is a "shared hallucination", in which case, the question of what is "real" becomes complicated because it is no longer a black-and-white issue. The idealist and the materialist, alike, are always going to be coming back to the same four questions, though: What can we categorize? What can we explain? What can we predict? What can we control?

At first glance, I thought this was going to be a counter-argument to the "modern AI language models are like aliens who have just landed on Earth" comparison, then I remembered we're in a weirder timeline where people are actually talking about literal aliens as well 🙃

To add more on "what we don't see": if some UAPs are aliens, why have they been on earth for decades, but they haven't done anything yet other than fly around? Why have they never landed (or, if they've landed, why did they only land at secret military bases)? My prior is that if intelligent aliens visited earth, they would do one of two things:

  1. They arrive in force, and their presence quickly becomes undeniable.
  2. Their scouts arrive and fly around for only a short time.

It seems a lot less likely that they'd arrive, fly around for decades, get spotted several times, but only ever in the distance.

What I like about the UFO-stuff is that like early Covid it is a nice benchmark to see which public pundits are thinking clearly and which aren't. 

Often if public pundits make a call, it requires detailed knowledge of some kind - which means that I can't really assess it and it's not clear how well the ability to make this call generalises to other issues. 

But the UFOs and early Covid are pretty uncomplicated, I think they give a decent signal how calibrated someone is. 

(he said cleverly neglecting to state whether aliens are likely or unlikely)

It's not a take that I've thought about deeply, but could the evidence be explained by a technological advancement: the ability to hop between diverging universes?

  • It would explain why we don't see aliens; they discover the technology, and that empty parallel worlds are closer in terms of energy expenditure.

  • It could also explain why the interlopers don't bother us much; they are scouting for uninhabited parallel earths with easily-accessible resources, and skipping those with a population. The only ones we see are the ones incompetent or unlucky enough to crash.

  • It would explain why aliens aren't ridiculously outclassing us technologically. They don't have to solve interstellar travel before they start hopping.

  • It would provide an alternate explanation for why aliens 'look like us'; they are from timelines with varying amounts of divergence. (The default explanation of course being that we are primed to see humans everywhere, so our imagined monsters look human.)

I can easily think of a few arguments against this possibility.

  • If dimension hoppers aren't far ahead of us technologically, trading with us has advantages. Why skip, instead of open trade?

  • Technology would probably continue to advance. Hyper-advanced dimension hoppers should be better capable of scouting dimensions, and of displacing populated worlds, and yet we don't see them. (Perhaps they are better at hiding, but then, they don't need to hide.)

  • Instead of 'where is the alien AI' we are now left with 'where is the divergent timeline AI'.

That last one in particular makes me think this explanation isn't likely. I'd expect rogue AI and self-replicating machines to be invading constantly.

‘Dimension hopping’ or ‘dimension manipulation’ could be a solution to the Fermi paradox. The universe could be full of intelligent life that remain silent and (mostly) invisible behind advanced spatial technology.

(the second type refers to more limited hypothetical dimension technology such as creating pocket dimensions, for example, rather than accessing other universes)

My rather marginal view is that both UFO and BigFoot is the same phenomenon which can appear only in the sitiations of "low concentration of human attention". In some sense it is similar to large-scale Schrodinger's cat, which can be in the state of both alive and dead only when unobserved.

This explains why there are many evidence but never conclusive evidence. 

Could you clarify whether you attribute the similarity to a) how human minds work, or b) how the physical world works, or c) something I am not thinking of?

b would seem clearly mistaken to me:

In some sense it is similar to large-scale Schrodinger's cat, which can be in the state of both alive and dead only when unobserved.

For this I would recommend to use the decoherence conception of what measurements do (which is the natural choice in the Many Worlds Interpretation and still highly relevant if one assumes that a physical collapse occurs during measurement processes). From this perspective, what any measurement does is to separate the wave function into a bunch of contributions where each contains the measurement device showing result x and the measured system having the property x that is being measured[1]. Due to the high-dimensional space that the wave-function moves in, these parts will tend to never meet again, and this is what the classical limit means[2]. When people talk about 'observation' here, it is important to realize that an arbitrary physical interaction with the outside world is sufficient to count. This includes air molecules, thermal radiation, cosmic radiation, and very likely even gravity[3]. For objects large enough that we can see them, it will not happen without extreme effort that they remain 'unobserved' for longer times[4].

For anything macroscopic, there is no reason to believe that "human observation" is remotely relevant for observing classical behaviour.

  1. This assumes that this is a useful measurement. More generally, any arbitrary interaction between two systems does the same thing except that there is no legible "result x" or "property x" which we could make use of. ↩︎

  2. of course, if there is a collapse which actually removes most of the parts there is additional reason why they will not meet in the future. The measurements we have done so far do not show any indication of a collapse in the regimes we could access, which implies that this process of decoherence is sufficient as a description for everyday behaviour. The reason why we cannot access further regimes is that decoherence kicks in and makes the behaviour classical even without the need for a physical collapse. ↩︎

  3. Though getting towards experiments which manage to remove the other decoherence sources enough that gravity's decoherence even could be observed is one of the large goals that researchers are striving for. ↩︎

  4. E.g. Decoherence and the Quantum-to-Classical Transition by Maximilan Schlosshauer has a nice derivation and numbers for the 'not-being-observed' time scales: Table 3.2 gives the time scales resulting from different 'observers' for a dust grain of size 0.01 mm as "1 s due to cosmic background radiation, s from photons at room temperature, s from collisions with air molecules". ↩︎

Sabina Hossenfelder argues against the idea decoherence is measurement e.g. here:  As I understand, the main difference form her view is that decoherence is the relation between objects in the system, but measurement is related to the whole system "collapse".

I think (give like 30 per cent probability) that the general nature of the UFO phenomenon is that it is anti-epistemic, that it, it actively prevents our ability to get definite knowledge about about it. How exactly this happens is not clear, and there could be several ideas. 

One idea (it will be quantum woo, I know) which I find attractive is that other observers are in the situation of  Wigner friend.  A remote observer in the such state can interact with other non-collapsed objects. But the only way I can learn about this is getting some strange stories after this remote observer was observed by me and "collapsed". However, I can't personally observe such high strangeness events. This put a limit on the power of evidence I can get about hight strangeness phenomena. 

Note that by "collapse" I mean here not an observation of a single object inside the universe, but my observation of the whole universe, which fully collapses it. 

I think (give like 30 per cent probability) that the general nature of the UFO phenomenon is that it is anti-epistemic, that it, it actively prevents our ability to get definite knowledge about about it. How exactly this happens is not clear, and there could be several ideas. 

Something jumped out at me here.  Regardless of the explanation, there's a testable experiment in the works here.  We could confirm or falsify this anti-epistemic property.

Setup: find the 'base rate' of UFO sightings, how often do humans and aircraft sensors see them.  Then determine how large of an area you need to cover.

Cover half an area sufficiently large with thousands/millions of constantly recording high resolution cameras.  Use AI to check the footage for UFOs.

The other half is your control region.  Elicit UFO reports in both regions.  (you might put the cameras in both regions but not power the ones in the control region so human reporters don't know which region they are in)

Prediction: if UFOs are anti-epistemic, you will get no UFO reports from the region covered by cameras, and you will get a statistically meaningful number (because you chose a large enough collection area with enough people) from the control region.  

If the cameras ever pick up anything it will be blurry and distant, of course.

Obviously you then swap the groups and run the cameras in the control region.

It would be weird if reality works this way, and we can debate theories after empirical confirmation, but it already is weird in many other ways.

Really interesting idea.

We could check already existing data from e.g. parapsychology for this effect. As I remember, it was observed there that the stronger is control in the experiments, the less is co-called psi-effect which usually was interpreted as evidence against psi.

But suspect that that meta-anti-epistemic nature of the phenomena will appear even in such setup and it will produce initially promising but then declining results.

Sabina Hossenfelder argues against the idea decoherence is measurement e.g. here:  As I understand, the main difference form her view is that decoherence is the relation between objects in the system, but measurement is related to the whole system "collapse".

What she's mainly arguing there is that decoherence does not solve the measurement problem because it does not result in the Born rule without further assumptions.  She also links another post where she argues that attempts to derive the Born rule via rational choice theory are non-reductionist.

It might be that she thinks that means that some separate collapse is likely in addition to the separation into a mixture via decoherence, where the collapse selects a particular outcome from the mixture, but even if that were true, such a collapse would, I think, have to occur after or simultaneously with decoherence or it would be observable.

None of this leads, as far as I can tell, to the strange expectations that you seem to have.

As I understand, the main difference form her view is that decoherence is the relation between objects in the system, but measurement is related to the whole system "collapse".

I think I would agree to "decoherence does not solve the measurement problem" as the measurement problem has different sub-problems. One corresponds to the measurement postulate which different interpretations address differently and which Sabine Hossenfelder is mostly referring to in the video. But the other one is the question of why the typical measurement result looks like a classical world - and this is where decoherence is extremely powerful: it works so well that we do not have any measurements which manage to distinguish between the hypotheses of

  • "only the expected decoherence, no collapse"
  • "the expected decoherence, but additional collapse"

With regards to her example of Schrödinger's cat, this means that the state will not actually occur. It will always be a state where the environment must be part of the equation such that the state is more like after a nanosecond and already includes any surrounding humans after a microsecond (light went 300 m in all directions by then). When human perception starts being relevant, the state is With regards to the first part of the measurement problem, this is not yet a solution. As such I would agree with Sabine Hossenfelder. But it does take away a lot of the weirdness because there is no branch on the wave function that contains non-classical behaviour[1].

Wigner's friend.

You got me here. I did not follow the large debate around Wigner's friend as i) this is not the topic I should spend huge amounts of time on, and ii) my expectations were that these will "boil down to normality" once I manage to understand all of the details of what is being discussed anyway.

It can of course be that people would convince me otherwise, but before that happens I do not see how these types of situations could lead to strange behaviour that isn't already part of the well-established examples such as Schrödinger's cat. Structurally, they only differ in that there are multiple subsequent 'measurements', and this can only create new problems if the formalism used for measurements is the source. I am confident that the many worlds and Bohmian interpretations do not lead to weirdness in measurements[2], such that I am as-of-yet not convinced.

I think (give like 30 per cent probability) that the general nature of the UFO phenomenon is that it is anti-epistemic

Thanks for clarifying! (I take this to be mostly 'b) physical world' in that it isn't 'humans have bad epistemics') Given the argument of the OP, I would at least agree that the remaining probability mass for UFOs/weirdness as a physical thing is on the cases where the weird things do mess with our perception, sensors and/or epistemics.

The difficult thing about such hypotheses is that they can quickly evolve to being able to explain anything and becoming worthless as a world-model.

  1. This will generally be the case for any practical purposes. Mathematically, there will be minute contributions away from classicality. ↩︎

  2. at least not to this type of weirdness ↩︎

My hand wavy view is that 'consciousness' which causes collapse is a very small (collapse resistant as Chalmers wrote) object inside the brain. For example, it is an electric potential of membrane of a single neuron. As a result, everything outside it  - the whole universe - is in some sense the Schrödinger cat. 

The whole 'macroscopic quantum effects' are interferences between whole universes branches from the view of this small quantum object in they brain. It could be rephrased as small quantum object in the brain is itself in complex quantum states which may sound more plausibly.

Because the interference is happening between whole branches, photon-cause decoherence of some objects inside each branch is not relevant. 

This is why Everett called his theory relative interpretation of QM: there is a relation (multiplication of vectors states) between two systems, observer and the universe. Note that later "many worlds interpretation" is oversimplification of this idea as it excludes interference between branches.

One aspect which I disagree with is that collapse is the important thing to look at. Decoherence is sufficient to get classical behaviour on the branches of the wave function. There is no need to consider collapse if we care about 'weird' vs. classical behaviour. This is still the case even if the whole universe is collapse-resistant (as is the case in the many worlds interpretation). The point of this is that true cat states ( = superposed universe branches) do not look weird.

The whole 'macroscopic quantum effects' are interferences between whole universes branches from the view of this small quantum object in they brain.

Superposition of universe - We can certainly regard the possibility that the macroscopic world is in a superposition as seen from our brain. This is what we should expect (absent collapse) just from the sizes of universe and brain:

  1. The size of our brain corresponds to a limited number for the dimensionality of all possible brain states (we can include all sub-atomic particles for this)
  2. If the number of branches of the universe is larger than the number of possible brain states, there is no possible wave function in which there aren't some contributions in which the universe is in a superposition with regards to the brain. Some brain states must be associated with multiple branches.
  3. the universe is a lot larger than the brain and dimensionality scales exponentially with particle number
  4. further, it seems highly likely that many physical brain-states correspond to identical mind states (some unnoticeable vibration propagating through my body does not seem to scramble my thinking very much)

Because of this, anyone following the many worlds interpretation should agree that from our perspective, the universe is always in a superposition - no unknown brain properties required. But due to decoherence (and assuming that branches will not meet), this makes no difference and we can replace the superposition with a probability distribution.

Perhaps this is captured by your "why Everett called his theory relative interpretation of QM" - I did not read his original works.

The question now becomes the interference between whole universe branches: A deep assumption in quantum theory is locality which implies that two branches must be equal in all properties[1] in order to interfere[2]. Because of this, interference of branches can only look like "things evolving in a weird direction" (double slit experiment) and not like "we encounter a wholly different branch of reality" (fictional stories where people meet their alternate-reality versions).

Because of this, I do not see how quantum mechanics could create the weird effects that it is supposed to explain.

If we do assume that human minds have an extra ability to facilitate interaction between otherwise distant branches if they are in a superposition compared to us, this of course could create a lot of weirdness. But this seems like a huge claim to me that would depart massively from much of what current physics believes. Without a much more specific model, this feels closer to a non-explanation than to an explanation.

  1. more strictly: must have mutual support in phase-space. For non-physicists: a point in phase-space is how classical mechanics describes a world. ↩︎

  2. This is not a necessary property of quantum theories, but it is one of the core assumptions used in e.g. the standard model. People who explore quantum gravity do consider theories which soften this assumption ↩︎